What it's for
In NSP, the Timing - Fuel Composition Correction table holds the ignition timing change you want for ethanol fuel. The Fuel Composition Scalar decides how much of that correction is actually applied, as a percentage, based on the ethanol content measured by a fuel composition sensor. At 0% none of the correction is used; at 100% all of it is. In between, it blends.
You only need it on a flex fuel setup with a sensor such as the Haltech flex fuel composition sensor fitted.
What to check
- The sensor reads sensibly: close to 0% on ethanol-free gasoline (most US pump gas already contains around 10%) and close to your known blend on E85.
- The scalar reaches 100% at the ethanol content your timing correction was tuned on.
- The blend is smooth, with no sudden jumps that could shift timing abruptly as the tank changes.
- Knock logs stay clean at mixed blends, not just at the ends.
See also ignition fuel composition correction and the flex fuel tuning guide.
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